The Healthy People 2010 target for overweight among 6-11 year old children is five percent (Objective 19-3a). This leading health indicator, however, is moving at increasing distance from public health goals with 15 percent of US children currently overweight. The emerging epidemic of overweight among children underscores the need to identify contributing environmental factors. Marketplace trends for excessive and growing portion sizes in and outside the home have reinforced concerns that large portions may directly contribute to this problem by promoting excessive intake. Empirical investigation of portion size effects on children's eating, however, has been extremely limited. Two similarly designed studies provided initial evidence that serving large portions of an entree stimulated consumption at meals. However, the scope and nature of portion size influences on eating remain unclear;whether effects on intake generalize across foods, energy density and preference is unknown as is the mean(s) by which large portions cause excessive intake. Of particular public health interest is whether serving large portions may affect children's intake of sweetened beverages, fruits and vegetables, and energy dense foods. The proposed research involves a series of four experiments designed to address five broad aims. The first three experiments will evaluate scope of portion size effects by evaluating: (1) the effect of portion size on children's consumption of sweetened beverages;(2) the effect of portion size on children's intake of fruits and vegetables (FV) and whether such effects are moderated by children's FV preferences and;(3) whether the energy density of foods acts additively with portion size to affect children's energy consumption. A fourth experiment will begin to identify mechanisms by which large portions may promote excessive intake by investigating: (1) the effect of portion size on eating duration and rate as well as bite size and frequency and (2) the effects of plate size on children's response to large portions. The proposed investigation directly addresses the objectives of NIH PA-04-033, Diet Composition and Energy Balance, by initiating a series of short-term studies to systematically evaluate the effects of portion size on caloric intake in young children. This research will produce new data to clarify the public health significance of this potentially obesigenic influence. The results of this basic behavioral investigation may be used to inform the design of long-term studies on the effects of portion size on children's energy consumption and weight. Further, these basic research findings may also be used to develop interventions aimed at modifying potentially obesigenic aspects of young children's environments. Finally, findings will provide a scientific basis for anticipatory guidance to parents of young children regarding appropriate portion size.